[英]Three Threads Comnunition and Synchronize
背景:我有三個主題。 ThreadA負責將元素寫入隊列,如果隊列已滿,則通知ThreadC從隊列中讀取元素。 ThreadB是另一個條件,如果隊列未滿,但是時間超過5秒,則Thread通知threadC從隊列中獲取元素,最后,ThreadC通知ThreadB刷新其時間戳。
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Main {
private Lock lock = new ReentrantLock();
private Condition conA = lock.newCondition();
private Condition conB = lock.newCondition();
private Condition conC = lock.newCondition();
ArrayBlockingQueue<Integer> readQueueA = new ArrayBlockingQueue<>(3);
public static void main(String[] args) {
Main main1 = new Main();
try {
ThreadA threadWrite = main1.new ThreadA();
Thread threadOut = new Thread(threadWrite);
threadOut.start();
ThreadB threadB = main1.new ThreadB();
Thread threadBB = new Thread(threadB);
threadBB.start();
ThreadC threadRead = main1.new ThreadC();
Thread threadIn = new Thread(threadRead);
threadIn.start();
} catch (Exception ex) {
ex.printStackTrace();
}
}
class ThreadA implements Runnable {
public void addElement(Integer i) {
try {
readQueueA.put(i);
} catch (Exception ex ){
ex.printStackTrace();
}
}
@Override
public void run() {
int i = 0;
while (i < 10) {
lock.lock();
try {
if (readQueueA.size() < 3) {
addElement(i++);
} else {
System.out.println("notice C: " + new Date());
conC.signal();
conA.await();
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
lock.unlock();
}
}
}
}
class ThreadB implements Runnable {
@Override
public void run() {
reSetStartTime();
while (true) {
lock.lock();
try {
if (!conB.await(5, TimeUnit.SECONDS)) {
System.out.println("Timeout Zzzzzzz: " + new Date());
conC.signal();
} else {
System.out.println("RefreshB。。。。" + new Date());
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
lock.unlock();
}
}
}
}
class ThreadC implements Runnable {
public void printQueue(ArrayBlockingQueue<Integer> printQueue) {
int len = printQueue.size();
System.out.println("Queen Size :" + printQueue.size());
for (int i = 0; i < len; i++) {
System.out.print(printQueue.poll());
}
System.out.println();
}
@Override
public void run() {
while (true) {
lock.lock();
try {
System.out.println("I'm thread C " + new Date());
conC.await();
System.out.println("I'm thread C, and I wake up " + new Date());
if (readQueueA.size() > 0) {
System.out.print("OUTPUT: ");
printQueue(readQueueA);
conA.signal();
conB.signal();
} else {
System.out.println("No elements");
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
lock.unlock();
}
}
}
}
}
輸出:
"C:\Program Files\Java\jdk1.8.0_181\bin\java.exe"
notice C: Fri Sep 21 10:07:35 CST 2018
I'm thread C Fri Sep 21 10:07:35 CST 2018
TimeOut Zzzzzzz: Fri Sep 21 10:07:40 CST 2018
I'm thread C, and I wake up Fri Sep 21 10:07:40 CST 2018
OUTPUT: Queen Size :3
012
I'm thread C Fri Sep 21 10:07:40 CST 2018
notice C: Fri Sep 21 10:07:40 CST 2018
RefreshB。。。。Fri Sep 21 10:07:40 CST 2018
I'm thread C, and I wake up Fri Sep 21 10:07:40 CST 2018
OUTPUT: Queen Size :3
345
I'm thread C Fri Sep 21 10:07:40 CST 2018
notice C: Fri Sep 21 10:07:40 CST 2018
RefreshB。。。。Fri Sep 21 10:07:40 CST 2018
I'm thread C, and I wake up Fri Sep 21 10:07:40 CST 2018
OUTPUT: Queen Size :3
678
I'm thread C Fri Sep 21 10:07:40 CST 2018
RefreshB。。。。Fri Sep 21 10:07:40 CST 2018
TimeOut Zzzzzzz: Fri Sep 21 10:07:45 CST 2018
I'm thread C, and I wake up Fri Sep 21 10:07:45 CST 2018
OUTPUT: Queen Size :1
9
I'm thread C Fri Sep 21 10:07:45 CST 2018
RefreshB。。。。Fri Sep 21 10:07:45 CST 2018
TimeOut Zzzzzzz: Fri Sep 21 10:07:50 CST 2018
I'm thread C, and I wake up Fri Sep 21 10:07:50 CST 2018
No elements
....
但是輸出不是我所期望的,為什么首先是ThreadB outPut TimeOut Zzz ?我認為應該不輸出該項目。 5s。有人可以幫我解釋或解決它嗎? 感謝你!
預期:
notice C: Fri Sep 21 10:28:31 CST 2018
I'm thread C Fri Sep 21 10:28:**31** CST 2018
I'm thread C, and I wake up Fri Sep 21 10:28:31 CST 2018
OUTPUT: Queen Size :3
012
I'm thread C Fri Sep 21 10:28:31 CST 2018
notice C: Fri Sep 21 10:28:31 CST 2018
RefreshB。。。。Fri Sep 21 10:28:31 CST 2018
...
這是在您發布的特定情況下發生的情況:A啟動,運行while循環,直到發出C信號並等待。 然后,C啟動並等待,從而出現問題。 在 C開始等待之前發出了一個信號,因此該信號呼叫丟失了,現在A和C都在等待。 所以在這一點上,控制台上是
通知C ...
我是線程C ...
現在,B啟動,並等待整整5秒鍾,因為沒有其他線程可發出信號。 這樣, conB.await(5, TimeUnit.SECONDS)
返回false,它輸出Timeout Zzzzzzz:
然后向C發出信號。這就是為什么事情看起來Timeout Zzzzzzz:
的原因,只有在另一個線程已經在等待時,信號才有效!
要解決此問題,請嘗試更改
conC.await();
System.out.println("I'm thread C, and I wake up " + new Date());
至
if (readQueueA.size() < 3) {
conC.await();
System.out.println("I'm thread C, and I wake up " + new Date());
}
這樣,如果等待條件已經滿足,C就不會等待。
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